The X-ray emission from Al and Cu plasma generated by femtosecond and nanosecond laser pulses have been measured and comparied. The irradiaton intensities of fs and ns laser pulses are 8.9×1015 and 3.8×1011 W/cm2 respectively. The experimental results show that under fs laser irradiation the emission peak is shifted to shorter wavelength. The ionization stage and temperature of fs Al Plasma is higher than that produced by ns laser.